Preparation of highly transparent superconductor-semiconductor contacts

In this report we present a procedure to fabricate highly transmissive supe rconducting Nb-In0.77Ga0.23As contacts. A combination of a sulphur passivat ion of the etched semiconductor prior to the deposition of Nb and an anneal ing step is used. To quantitatively classify the transparency of the contac ts, transport measurements of the differential conductance are carried out at 300 mK and compared with a model given by Blonder, Tinkham, and Klapwijk [Phys. Rev. B 25, 4515 (1981)]. The procedure yields almost ideal supercon ductor-semiconductor contacts. Additionally, a high reproducibility of the contact transparency is achieved. The results are interpreted in terms of d iffusion of In in both the niobium and the In0.77Ga0.23As. (C) 2000 America n Institute of Physics. [S0021- 8979(00)05318-4].